1. Field of the Invention
This invention relates to apparatus and methods for forming an elongated product and, more particularly, to apparatus and methods for deforming a workpiece so as to produce an elongated product, which product may be composed of one or more individual elongated articles, where the overall cross-sectional shape of the product differs from that of the workpiece.
2. Description of the Prior Art
In the art of forming elongated products, it is known to utilize hydrostatic extrusion techniques, wherein hydrostatic pressure is applied to a workpiece within a chamber such that the material of the workpiece is rendered more ductile as the billet is forced through an aperture in a die located at one end of the chamber. Some examples of such techniques may be found in my U.S. Pat. No. Re. 28,795, in my copending application, Ser. No. 612,875, filed Sept. 12, 1975, and entitled, "Continuous Extrusion", and in my copending application, Ser. No. 664,611, filed Mar. 8, 1976, and entitled "Apparatus and Methods for Continuous Extrusion".
It is also known in such art to provide apparatus which includes a die having a plurality of apertures extending therethrough, and to force a workpiece through such die, e.g., by the hydrostatic extrusion techniques disclosed in my previously mentioned patent and applications, so as to produce simultaneously a plurality of elongated articles. For example, one such die is disclosed in my U.S. Pat. No. 3,948,079. Other such dies are disclosed in my copending applications entitled, "Apparatus and Methods for Forming Multiple Elongated Products" (Ser. No. 638,493) and "Apparatus and Methods for Forming a Plurality of Elongated Products" (Ser. No. 638,495), both filed on Dec. 8, 1975.
In my copending application, Ser. No. 638,494, also filed on Dec. 8, 1975, and entitled, "Methods and Apparatus for Forming and Handling Elongated Products", I teach the use of a suitably shaped die for deforming a workpiece, e.g., by the previously described hydrostatic extrusion techniques, in order to produce an integral structure, such as a tape, composed of the material of the workpiece. Such integral structure includes a number of elongated articles extending in parallel plus additional interconnecting material joining the elongated articles together into a single elongated product for simplified handling, prior to dissociation into individual elongated articles. Additionally, in my copending application, Ser. No. 670,467, filed Mar. 25, 1976 and entitled, "Methods and Apparatus for Forming Wire Tapes", I disclose alternative techniques for forming such a tape.
In many instances, the overall cross-sectional shape of the product of an extrusion process, whether such product be a single article or a number of simultaneously formed articles, differs from the initial cross-sectional shape of the workpiece. Such difference in shape is characteristic, for example, of my previously mentioned applications, Ser. Nos. 638,493, 638,494, and 638,495, all of which were filed on Dec. 8, 1975, and Ser. No. 670,467, filed Mar. 25, 1976. The use of conventional types of extrusion dies, having tapering entry walls of conical shape, leading to appropriately configured apertures cut through the die centers, has not proved particularly satisfactory where such changes in shape during extrusion have been involved. It has been noted, for example, that the extrusion pressures required have generally been higher in such cases than in the case of round-to-round extrusions at equivalent reduction ratios with similar tapering die entry walls of conical shape. Such increased pressure levels are believed to result from the fact that, as the cross-section of a workpiece undergoes reshaping during extrusion, the material at the radially outermost edges of the workpiece tends to attain its final size sooner than does the material toward the center of the workpiece. Thus, as the more central material continues to undergo plastic deformation, the resulting internal pressure in the workpiece causes the radially outermost edge material to swell outwardly against the die aperture boundary surfaces, causing additional frictional drag.
U.S. Pat. No. 3,583,204 to J. Nilsson discloses a die for forming a product having a cross-sectional shape which differs from that of a workpiece employed, which die does not utilize the conventional conical entry wall configuration. Instead, a conical first part tapers inwardly, at a 45.degree. apex angle, into a chisel-shaped second part, with a 90.degree. apex angle, leading to an aperture of rectangular configuration. The previously discussed, premature attainment of final size along the radially outermost edges of the workpiece, is apparently characteristic also of the Nilsson die. Moreover, a degree of redundant work is believed introduced by the configuration of the Nilsson die, by virtue of the two part arrangement. In particular, since each element of the material of the workpiece is twice redirected prior to reaching the rectangular die aperture, i.e., once upon entering into the 45.degree. conical first part and once upon entering into the 90.degree. chisel-shaped second part, the work involved in changing direction of the workpiece element is greater than that required by a direct, straight line flow of workpiece material along a die entry wall. Thus, the use of the Nilsson die apparently requires relatively high operating pressures.
Accordingly, there is a clear need for apparatus and methods wherein relatively low operating pressures are required in order to deform a workpiece into a product, composed of one or more individual articles, with an overall cross-sectional shape differing from that of the workpiece.